Polymerization product pressures in olefin polymerization

ABSTRACT

A process for making a low density polymer in a polymerization reactor system, the process comprising polymerizing an olefin monomer, and optionally an olefin comonomer, in the presence of a diluent in a polymerization reactor to make a polymerization product slurry consisting of a liquid phase and a solid phase, wherein the solid phase comprises an olefin polymer having a density of between about 0.905 g/cm 3  to about 0.945 g/cm 3 ; and discharging the polymerization product slurry from the polymerization reactor through a continuous take-off valve to make a mixture further comprising a vapor phase. The mixture comprises a pressure less than a bubble point pressure of a component in the polymerization product slurry.

CROSS-REFERENCE TO RELATED APPLICATIONS

Not applicable.

STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT

Not applicable.

REFERENCE TO A MICROFICHE APPENDIX

Not applicable.

FIELD

This disclosure relates to the management of pressures downstream of apolymerization reactor.

BACKGROUND

Polyolefins such as polyethylene and polypropylene may be prepared byslurry polymerization. In this technique, feed materials such asdiluent, monomer and catalyst are introduced to a loop reaction zone,forming a slurry in the reaction zone. In continuous loop reactors, theslurry circulates through the loop reaction zone, and the monomer reactsat the catalyst in a polymerization reaction. The polymerizationreaction yields solid polyolefins in the slurry. A polymerizationproduct having solid polyolefins is then transferred from the reactorand separated to recover the solid polyolefins. Operating pressuresduring transfer of the product can affect recovery of solid polyolefins;thus, pressure management can be important.

SUMMARY

Disclosed is a process for making a low density polymer in apolymerization reactor system, the process comprising polymerizing anolefin monomer, and optionally an olefin comonomer, in the presence of adiluent in a polymerization reactor to make a polymerization productslurry consisting of a liquid phase and a solid phase, wherein the solidphase comprises an olefin polymer having a density of between about0.905 g/cm³ to about 0.945 g/cm³; and discharging the polymerizationproduct slurry from the polymerization reactor through a continuoustake-off valve to make a mixture further comprising a vapor phase.

In another aspect, disclosed is a process for pressure management of apolymerization product slurry withdrawn from a loop polymerizationreactor in slurry polymerization, the process comprising conveying thepolymerization product slurry through a continuous take-off valve,wherein the polymerization product slurry comprises a liquid phase and asolid phase; converting the polymerization product slurry to a mixture,wherein the mixture comprises at least a portion of the liquid phase,the solid phase, and a vapor phase; and conveying the mixture through aflashline heater; wherein, at least at one location downstream of thecontinuous take-off valve, the mixture comprises a pressure less than abubble point pressure of the liquid phase.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a process flow diagram of an embodiment of a polymerizationreactor system according to the disclosure.

FIG. 2 shows a cross-sectional view of an embodiment of a portion of theflashline heater, taken along sight line 2-2 of FIG. 1.

DETAILED DESCRIPTION OF THE EMBODIMENTS

Disclosed herein are embodiments of a polymerization reactor system.Additionally, disclosed herein are processes for making low densitypolymers in the polymerization reactor system and for pressuremanagement of a polymerization product flowing from a looppolymerization reactor to a separation vessel in slurry polymerization.

FIG. 1 shows a process flow diagram of an embodiment of a polymerizationreactor system 100 according to the disclosure. The system 100 maycomprise a polymerization reactor 110 which forms a polymerizationproduct, a first line 120 which receives a polymerization product (e.g.,as a polymerization product slurry which is discharged from thepolymerization reactor 110), a second line 130 which receives thepolymerization product (e.g., as a mixture) from the first line 120, aseparation vessel 140 which receives the polymerization product (e.g.,as a gas phase mixture) from the second line 130, a control system 160to control various components of the system 100, or combinationsthereof. Solid polymer may be recovered from the separation vessel 140.The first line 120 may comprise a continuous take-off valve 122. Thesecond line 130 may comprise a flashline heater 132.

As used herein, the terms “polymerization reactor” or “reactor” mayinclude at least one loop slurry polymerization reactor capable ofpolymerizing olefin monomers, and optionally olefin comonomers, toproduce homopolymers (e.g., polyethylene), or optionally, copolymers(e.g., polyethylene copolymer). Such homopolymers and copolymers may bereferred to as resins or polymers.

In one or more of the embodiments disclosed herein, the reactor 110 maycomprise any vessel or combination of vessels suitably configured toprovide an environment for a chemical reaction (e.g., a contact zone)for monomers (e.g., ethylene) and/or polymers (e.g., an “active” orgrowing polymer chain), and optionally comonomers (e.g., 1-butene,1-hexene, 1-octene, or combinations thereof) and/or copolymers, in thepresence of a catalyst to yield a polymer (e.g., a polyethylene polymer)and/or copolymer.

In additional or alternative embodiments, the reactor 110 may polymerizeolefin monomers, and optionally olefin comonomers, in the presence of adiluent to make a polymerization product slurry comprising a solid phaseand a liquid phase, wherein the solid phase comprises an olefin polymerhaving a density as disclosed herein.

The polymerization processes performed in the reactor(s) disclosedherein (e.g., reactor 110) may include batch or continuous processes.Continuous processes can use intermittent or continuous productdischarge. Processes may also include partial or full direct recycle ofunreacted monomer, unreacted comonomer, and/or diluent.

According to one aspect, the loop slurry polymerization reactor 110 maycomprise vertical or horizontal pipes 112 and 114 interconnected bysmooth bends or elbows 115, which together form a loop. Portions of theloop slurry polymerization reactor 110, such as pipes 112, may havecooling jackets 113 placed therearound to remove excess heat generatedby the exothermic polymerization reactions. A cooling fluid may becirculated through jackets 113, for example.

A motive device, such as pump 150, may circulate the fluid slurry in theloop slurry polymerization reactor 110. An example of the pump 150 is anin-line axial flow pump with a pump impeller 152 disposed within theinterior of the reactor 140. The impeller 152 may, during operation,create a turbulent mixing zone within a reactor slurry circulatingthrough the reactor 110 such that sufficient contact between differentpolymerization components within the slurry may occur. The impeller 152may also assist in propelling the reactor slurry through the closed loopof the reactor 110 at sufficient speed to keep solid particulates, suchas the catalyst or solid polymer, suspended within the reactor slurry.The impeller 152 may be driven by a motor 154 or other motive force.

The system 100 may additionally comprise any equipment associated with apolymerization reactor, such as pumps, control devices (e.g., a PIDcontroller), measurement instruments (e.g., thermocouples, transducers,and flow meters), alternative inlet and outlet lines, etc.

A typical loop polymerization process is disclosed, for example, in U.S.Pat. Nos. 3,248,179, 4,501,885, 5,565,175, 5,575,979, 6,239,235,6,262,191 and 6,833,415, each of which is incorporated by reference inits entirety herein.

Although the embodiment illustrated in FIG. 1 shows a single reactor110, one of skill in the art viewing this disclosure will recognize thatany suitable number and/or configuration of reactors may be employed.

In embodiments having multiple reactors, production of polymerizationproduct in multiple reactors may include several stages in at least twoseparate polymerization reactors interconnected by a transfer devicemaking it possible to transfer the polymerization product resulting froma first polymerization reactor into a second reactor (e.g., loop slurrypolymerization reactor 110). The desired polymerization conditions inone reactor may be different from the polymerization conditions of theother reactor(s). Alternatively, polymerization in multiple reactors mayinclude the manual transfer of polymerization product (e.g., as apolymerization product slurry, as a mixture, as solid polymer, orcombinations thereof) from one reactor to subsequent reactors forcontinued polymerization. Multiple reactor systems may include anycombination including, but not limited to, multiple loop reactors, acombination of loop and gas reactors, multiple high pressure reactors ora combination of high pressure with loop and/or gas reactors. Themultiple reactors may be operated in series, in parallel, orcombinations thereof.

In embodiments having multiple reactors, various types of reactors thatmay additionally be included in system 100 may comprise loop slurrypolymerization reactors. Such reactors may have a loop configuration,such as the configuration of the loop slurry polymerization reactor 110of FIG. 1.

In embodiments having multiple reactors, various types of reactors thatmay additionally be included in system 100 may comprise gas-phasereactors. Gas-phase reactors may comprise fluidized bed reactors orstaged horizontal reactors. Gas-phase reactors may employ a continuousrecycle stream containing one or more monomers continuously cycledthrough a fluidized bed in the presence of the catalyst underpolymerization conditions. A recycle stream may be withdrawn from thefluidized bed and recycled back into the reactor. Simultaneously,polymerization product may be withdrawn from the reactor and new orfresh monomer may be added to replace the polymerized monomer. Likewise,copolymer product may optionally be withdrawn from the reactor and newor fresh comonomer may be added to replace polymerized comonomer,polymerized monomer, or combinations thereof. Such gas phase reactorsmay comprise a process for multi-step gas-phase polymerization ofolefins, in which olefins are polymerized in the gaseous phase in atleast two independent gas-phase polymerization zones while feeding acatalyst-containing polymer formed in a first polymerization zone to asecond polymerization zone. One type of gas phase reactor is disclosedin U.S. Pat. Nos. 5,352,749, 4,588,790 and 5,436,304, each of which isincorporated by reference in its entirety herein.

In embodiments having multiple reactors, various types of reactors thatmay additionally be included in system 100 may comprise high pressurereactors. High pressure reactors may comprise autoclave or tubularreactors. Tubular reactors may have several zones where fresh monomer(optionally, comonomer), initiators, or catalysts may be added. Monomer(optionally, comonomer) may be entrained in an inert gaseous stream andintroduced at one zone of the reactor. Initiators, catalysts, and/orcatalyst components may be entrained in a gaseous stream and introducedat another zone of the reactor. The gas streams may be intermixed forpolymerization. Heat and pressure may be employed appropriately toobtain optimal polymerization reaction conditions.

In embodiments having multiple reactors, various types of reactors thatmay additionally be included in system 100 may comprise a solutionpolymerization reactor wherein the monomer (optionally, comonomer) maybe contacted with the catalyst composition by suitable stirring or othermeans. A carrier comprising an inert organic diluent or excess monomer(optionally, comonomer) may be employed. If desired, the monomer and/oroptional comonomer may be brought in the vapor phase into contact withthe catalytic reaction product, in the presence or absence of liquidmaterial. The polymerization zone is maintained at temperatures andpressures that will result in the formation of a solution of the polymerin a reaction medium. Agitation may be employed to obtain bettertemperature control and to maintain uniform polymerization mixturesthroughout the polymerization zone. Adequate means are utilized fordissipating the exothermic heat of polymerization.

Conditions of a polymerization reactor, e.g., loop slurry polymerizationreactor 110, which may be chosen and even controlled for polymerizationefficiency and to provide resin properties include temperature, pressureand the concentrations of various reactants.

Polymerization temperature can affect catalyst productivity, polymermolecular weight and molecular weight distribution. Suitablepolymerization temperature may be any temperature below thede-polymerization temperature according to the Gibbs Free energyequation. Typically this includes from about 60° C. to about 280° C.,for example, and from about 70° C. to about 110° C., depending upon thetype of polymerization reactor.

Suitable pressures will also vary according to the reactor andpolymerization type. The pressure for liquid phase polymerizations in aloop reactor such as loop slurry polymerization reactor 110 is typicallyless than 1,000 psig, for example, about 650 psig. Pressure for gasphase polymerization is usually at about 100 to 500 psig. High pressurepolymerization in tubular or autoclave reactors is generally run atabout 20,000 to 75,000 psig.

Polymerization reactors can also be operated in a supercritical regionoccurring at generally higher temperatures and pressures. Operationabove the critical point of a pressure/temperature diagram(supercritical phase) may offer advantages.

In an embodiment, polymerization may occur in an environment having asuitable combination of temperature and pressure. For example,polymerization may occur at a pressure in a range of about 400 psi toabout 1,000 psi; alternatively, about 550 psi to about 650 psi,alternatively, about 600 psi to about 625 psi; and a temperature in arange of about 150° F. to about 130° F., alternatively, from about 195°F. to about 120° F.

The concentration of various reactants can be controlled to producesolid polymer with certain physical and mechanical properties. Theproposed end-use product that will be formed by the solid polymer andthe method of forming that product determines the desired properties.Mechanical properties include tensile, flexural, impact, creep, stressrelaxation and hardness tests. Physical properties include density,molecular weight, molecular weight distribution, melting temperature,glass transition temperature, temperature melt of crystallization,density, stereoregularity, crack growth, long chain branching andrheological measurements.

The concentrations and/or partial pressures of monomer, comonomer,hydrogen, co-catalyst, modifiers, and electron donors are important inproducing these resin properties. In embodiments, comonomer may be usedto control product density; hydrogen may be used to control productmolecular weight; cocatalysts can be used to alkylate, scavenge poisonsand control molecular weight; activator-support can be used to activateand support the catalyst; modifiers can be used to control productproperties; electron donors can be used to affect stereoregularity, themolecular weight distribution, or molecular weight; or combinationsthereof. In additional or alternative embodiments, the concentration ofpoisons may be minimized because poisons impact the reactions andproduct properties.

Polymerization reaction components of the reactor(s) disclosed herein(e.g., loop slurry polymerization reactor 110) may include monomers,comonomers, diluent, molecular weight control agents, catalyst,co-catalyst, any other desired co-reactants or additives, orcombinations thereof.

In embodiments, a monomer may comprise an olefin. In additional oralternative embodiments, a monomer may comprise an alpha olefin.Suitable olefins include, but are not limited to, ethylene andpropylene.

In embodiments, a comonomer may comprise an unsaturated olefin having 3to 12 carbon atoms. For example, suitable comonomers may include, butare not limited to, propylene, 1-butene, 1-hexene, 1-octene, orcombinations thereof.

In embodiments, a diluent may comprise unsaturated hydrocarbons having 3to 12 carbon atoms. In embodiments, suitable diluents used in slurrypolymerization processes may include, but are not limited to, themonomer being polymerized (examples described above), the comonomerbeing polymerized (examples described above), hydrocarbons that areliquids under reaction conditions, or combinations thereof. Furtherexamples of suitable diluents include, but are not limited to, propane,cyclohexane, isobutane, n-butane, n-pentane, isopentane, neopentane,n-hexane, or combinations thereof. Some loop polymerization reactionscan occur under bulk conditions where no diluent is used. An example ispolymerization of propylene monomer as disclosed in U.S. Pat. No.5,455,314, which is incorporated by reference herein in its entirety.

In embodiments, a suitable catalyst system for polymerizing the monomersand any comonomers may include, but is not limited to a catalyst(s) and,optionally, a co-catalyst(s) and/or a promoter(s). Nonlimiting examplesof suitable catalyst systems include Ziegler Natta catalysts, Zieglercatalysts, chromium catalysts, chromium oxide catalysts, chromocenecatalysts, metallocene catalysts, nickel catalysts, or combinationsthereof. Nonlimiting examples of co-catalyst include triethylboron,methylaluminoxane, alkyls such as triethylaluminum, or combinationsthereof. Suitable activator-supports may comprise solid super acidcompounds. Catalyst systems suitable for use in this disclosure havebeen described, for example, in U.S. Pat. No. 7,619,047 and U.S. PatentApplication Publication Nos. 2007/0197374, 2009/0004417, 2010/0029872,2006/0094590, and 2010/0041842, each of which is incorporated byreference herein in its entirety.

In embodiments, a molecular weight control agent may comprise hydrogen,cocatalyst, modifiers, other polymerization reaction componentsrecognized by one skilled in the art with the aid of this disclosure, orcombinations thereof.

The polymerization reaction components may be introduced to an interiorof the loop slurry polymerization reactor 110 via inlets or conduits atspecified locations, such as feed line 102. The reaction componentsidentified above (and others known to those skilled in the art with theaid of this disclosure) may form a suspension, i.e., a reactor slurry,that circulates through the loop formed by the loop slurrypolymerization reactor 110. Generally, continuous processes may comprisethe continuous introduction of polymerization components into the loopslurry polymerization reactor 110 and the continuous removal orwithdrawal (e.g., via first line 120) of a polymerization product.

The polymerization product may be withdrawn from one or more reactorspresent in system 100, e.g., the loop slurry polymerization reactor 110,via first line 120. The withdrawn polymerization product may be conveyedthrough the first line 120 to the second line 130 (e.g., conveyed via adrop in pressure). Collectively, lines 120 and 130 may be referred to asa flashline between reactor 110 and separation vessel 140, wherein aportion, substantially all, or all (e.g., 100%) of liquid phasecomponents present in the polymerization product are converted to gasphase components.

In embodiments such as the embodiment shown in FIG. 1, the first line120 of the system 100 may comprise a continuous take-off valve(hereinafter “CTO valve”) 122. In embodiments such as the embodimentshown in FIG. 1, the second line 130 may comprise a flashline heater132.

The polymerization product may be conveyed through the second line 130to the separation vessel 140. In embodiments, the second line 130 may bedownstream of the first line 120. In embodiments, the first line mayhave an inner diameter of about 1 inch to about 8 inches, and the secondline 130 may have an inner diameter of about 2 inches to about 10inches. For example, at least a portion of the second line 130 may havean inner diameter in a range from about 2 inches to about 10 incheswhich is greater than an inner diameter of the first line 120 in a rangefrom about 1 inch to about 8 inches. In additional embodiments, theinner diameter of the second line 130 may change (e.g., increase) alongthe length of the second line 130.

In embodiments, the polymerization product conveyed through first line120 and/or second line 130 may be in the form of a polymerizationproduct slurry, a mixture, or a gas phase product mixture. The form ofthe polymerization product (e.g., slurry, mixture, gas phase productmixture) may be a function of the conditions (e.g., temperature andpressure) present at a given location in lines 120 and 130.

In embodiments, the polymerization product slurry may convert to amixture in the first line 120, the second line 130, or both. In anembodiment, the polymerization product slurry converts to a mixture inthe first line 120. In an embodiment, the polymerization product slurrymay convert to a mixture at a location proximate to or within the CTOvalve 122. In an embodiment, the polymerization product slurry mayconvert to a mixture via a drop in pressure associated with the CTOvalve 122 of the first line 120. In an additional or alternativeembodiment, the mixture may then convert to a gas phase product mixtureas the polymerization product is conveyed through first line 120 and/orsecond line 130. In an additional or alternative embodiment, the mixturemay convert to a gas phase product mixture in the second line 130. In anadditional or alternative embodiment, the mixture may convert to a gasphase product mixture in the flashline heater 132 of the second line130. In embodiments, gas phase product mixtures may be present when gasphase reactors are used in place of or in addition to a loop slurryreactor.

In embodiments, the polymerization product slurry may comprise a solidphase and a liquid phase (e.g., a slurry of solid polymer and liquidphase diluent and/or monomer/comonomer (e.g., unreacted)). In additionalor alternative embodiments, the polymerization product slurry maycomprise one or more of hydrogen, nitrogen, methane, ethylene, ethane,propylene, propane, butane, isobutane, pentane, hexane, 1-hexene,octane, 1-octene, and heavier hydrocarbons.

In embodiments, the mixture may comprise at least a portion of theliquid phase, the solid phase, and a vapor phase (e.g., a three-phasemixture comprising liquid and gaseous diluent and/or monomer/comonomer(e.g., unreacted) and solid polymer). As the polymerization productslurry conveys through first line 120 and/or second line 130, a drop inpressure (e.g., associated with the CTO valve 122) in the first line120, a heat zone (e.g., associated with the flashline heater 132) in thesecond line 130, or both, may cause at least a portion of the liquidphase of the polymerization product slurry to vaporize to yield themixture comprising at least portion of the liquid phase (e.g., theremaining portion which is not vaporized at a given location in line 120or line 130), the solid phase (e.g., which was in the polymerizationproduct slurry), and a vapor phase comprising the vaporized portion ofthe liquid phase. In an embodiment, the vaporized portion includesportions of the liquid phase which vaporized from the polymerizationslurry to yield the mixture. In an additional or alternative embodiment,the vaporized portion includes a portion of the liquid phase whichvaporized from the mixture to yield a greater amount of the vapor phasein the mixture. In an embodiment, the liquid phase of the mixture maycomprise a remaining portion which is not vaporized. In embodiments, theremaining portion of the liquid phase in the mixture may comprise lessthan about 90%, 80%, 70%, 60%, 50%, 40%, 30%, 20%, 10%, or less byweight of the liquid phase in the polymerization product slurry.

In embodiments, the gas phase product mixture may comprise a vapor phaseand a solid phase (e.g., comprising solid polymer and vaporized diluentand/or monomer/comonomer (e.g., unreacted)). In an embodiment, the vaporphase may comprise the vaporized portion of the liquid phase whichvaporized from the mixture to yield the gas phase product mixture(inclusive or exclusive of liquid entrained within the solid polymer asdiscussed below). In an embodiment, the gas phase product mixture ispresent in the flashline heater 132 as the polymerization product istransferred to the separation vessel 140.

In embodiments, the solid phase may comprise various solids,semi-solids, or combinations thereof. In an embodiment, the solid phasemay comprise a solid polymer, a catalyst, a co-catalyst, or combinationsthereof. In embodiments, the solid polymer may comprise polyethyleneand/or a copolymer (e.g., polyethylene copolymer). In embodiments, thesolid polymer may comprise a homopolymer, a copolymer, or combinationsthereof. For example, the solid polymer may comprise a linear lowdensity polyethylene. The homopolymer and/or the polymers of thecopolymer may comprise a multimodal (e.g., a bimodal) polymer (e.g.,polyethylene). In embodiments, the solid polymer may comprise a densityless than about 0.945 g/cm³; alternatively, less than about 0.930 g/cm³;alternatively, less than about 0.925 g/cm³. In embodiments, the solidpolymer may comprise a density greater than about 0.905 g/cm³;alternatively, greater than about 0.910 g/cm³. In embodiments, the solidpolymer may comprise a density in the range of about 0.905 g/cm³ toabout 0.945 g/cm³; alternatively, in the range of about 0.912 g/cm³ toabout 0.925 g/cm³.

In embodiments, the liquid phase may comprise a diluent (e.g., unreacteddiluent), monomer (e.g., unreacted monomer), comonomer (e.g., unreactedcomonomer), or combinations thereof. In embodiments, the liquid phasemay comprise ethylene in a range of from about 0.1% to about 15%,alternatively, from about 1.5% to about 5%, alternatively, about 2% toabout 4% by total weight of the liquid phase of the polymerizationproduct. Ethane may be present in a range of from about 0.001% to about4%, alternatively, from about 0.2% to about 0.5% by total weight of thepolymerization product. Isobutane may be present in a range from about80% to about 98%, alternatively, from about 92% to about 96%,alternatively, about 95% by total weight of the polymerization product.

In embodiments, the vapor phase may comprise the vaporized portion ofthe liquid phase. In embodiments, the vapor phase may comprise a diluentvapor (e.g., unreacted diluent vapor), monomer vapor (e.g., unreactedmonomer vapor), comonomer vapor (e.g., unreacted comonomer vapor), orcombinations thereof.

As used herein, an “unreacted monomer,” for example, ethylene, refers toa monomer that was introduced into a polymerization reactor during apolymerization reaction but was not incorporated into a polymer. Inembodiments, the unreacted monomer may comprise ethylene, propylene,1-butene, 1-hexene, 1-octene, a heavier hydrocarbon having adouble-bonded carbon in the first position, or combinations thereof.

As used herein, an “unreacted comonomer,” refers to a comonomer that wasintroduced into a polymerization reactor during a polymerizationreaction but was not incorporated into a polymer. In embodiments, theunreacted comonomer may comprise propylene, 1-butene, 1-hexene,1-octene, a heavier hydrocarbon having a double-bonded carbon in thefirst position, or combinations thereof.

In embodiments, various lines may be used to connect the CTO valve 122in the first line 120. For example, line 124 may connect the CTO valve122 with the loop slurry polymerization reactor 110, and line 126 mayconnect the CTO valve 122 with the second line 130 (e.g., comprising theflashline heater 132). In alternative or additional embodiments, the CTOvalve 122 may connect directly or indirectly to the loop slurrypolymerization reactor 110. In alternative or additional embodiments,the CTO valve 122 may connect directly or indirectly to the flashlineheater 132. In embodiments, the CTO valve 122 may have a diameter ofabout 1 inch to about 8 inches.

In embodiments, various lines may be used to connect the flashlineheater 132 in the second line 130. For example, the flashline heater 132may connect directly to the first line 120, and line 134 may connect theflashline heater 132 to the separation vessel 140. In alternative oradditional embodiments, the flashline heater 132 may connect directly orindirectly to the first line 120. In alternative or additionalembodiments, the flashline heater 132 may connect directly or indirectlyto the separation vessel 140.

In the system 100 of FIG. 1, the first line 120 may have a drop inpressure, and the second line 130 may have a drop in pressure. In anembodiment, the drop in pressure of the first line 120 may be associatedwith the CTO valve 122. In an additional or alternative embodiment, thedrop in pressure of the second line 130 may be associated with theflashline heater 132.

The total drop in pressure between the loop slurry polymerizationreactor 110 and separation vessel 140 (i.e., the drop in pressure of thefirst line 120 summed with the drop in pressure of the second line 130)may comprises a drop in pressure from equal to or less than about 1,500psig in the reactor 110 to equal to or greater than about 50 psig in theseparation vessel 140; alternatively, a drop from equal to or less thanabout 1,000 psig to equal to or greater than about 100 psig;alternatively, a drop from equal to or less than about 650 psig togreater than or equal to about 135 psig. In an embodiment, the solidpolymer comprises polyethylene, the diluent comprises isobutane, and thetotal drop in pressure comprises a drop in pressure from about 650 psigequal to or greater than about 150 psig. In an embodiment, the solidpolymer comprises polypropylene, the diluent comprises isobutane, andthe total pressure differential comprises a drop in pressure from about650 psig to about 225 psig, alternatively, from about 650 psig to about240 psig.

In FIG. 1, the drop in pressure of first line 120 may be characterizedby a drop in pressure between any two pressures P₀, P₁, P₂, and P₃. Inan embodiment, the drop in pressure between P₁ and P₂ may be associatedwith the CTO valve 122. In an embodiment, the drop in pressureassociated with the CTO valve 122 may depend on the position (e.g.,valve rotation) of the valve, i.e., the degree by which the CTO valve122 is open. For example, the CTO valve 122 may have a valve rotation ofabout 5°, 10°, 20°, 30°, 40°, 50°, 60°, 70°, 80°, 90°, or more.

In an embodiment, the drop in pressure between P₁ and P₂ may comprise amajority of the drop in pressure of first line 120. In an additional oralternative embodiment, the drop in pressure between P₀ and P₂ maycomprise a majority of the drop in pressure of first line 120. In anadditional or alternative embodiment, the drop in pressure between P₁and P₃ may comprise a majority of the drop in pressure of first line120.

The drop in pressure of the second line 130 may be characterized by adrop in pressure between any two pressures P₃, P₄, and P₅. In anembodiment, the drop in pressure between P₃ and P₄ may be associatedwith the flashline heater 132.

In an embodiment, the drop in pressure between P₃ and P₄ may comprise amajority of the drop in pressure of the second line 130. In anadditional or alternative embodiment, the drop in pressure between P₃and P₅ may comprise a majority of the drop in pressure of the secondline 130. In an additional or alternative embodiment, the drop inpressure between P₄ and P₅ may comprise a majority of the drop inpressure of the second line 130.

In embodiments, the drop(s) in pressure of the first line 120 and secondline 130 provide means of conveyance of the polymerization productbetween the polymerization reactor 110 and the separation vessel 140.

In an embodiment, the polymerization product in the first line 120, thesecond line 130, or both, may be heated such that the solid polymer inthe polymerization product is conveyed through the first line 120 (e.g.,the CTO valve 122), the second line 130 (e.g., the flashline heater132), or both, at a temperature less than the melting temperature,softening temperature, swelling temperature, or combinations thereof, ofthe solid polymer in the polymerization product. In embodiments, theheating of the polymerization product may be controlled (e.g., viacontrol system 160).

In an embodiment, the melting temperature of the solid polymer maycomprise from about 180° F. to about 266° F.; alternatively, from about221° F. to about 266° F.; alternatively, from about 180° F. to about240° F.; alternatively, from about 221° F. to about 240° F.;alternatively, from about 248° F. to about 266° F. In an embodiment, thesolid polymer is conveyed through the first line 120, the second line130 (e.g., the flashline heater 132), or both, at a temperature belowthe temperature at which the solid polymer begins to melt, soften,swell, or combinations thereof.

In an embodiment, the solid polymer comprises polyethylene and theheating results in a solid polymer temperature of greater than or equalto about 0° F. and less than or equal to about 130° F.; alternatively,greater than or equal to about 0° F. and less than or equal to about180° F.

In an embodiment, the solid polymer comprises polypropylene and theheating results in a solid polymer temperature of greater than or equalto about 0° F. and less than or equal to about 250° F.; alternatively,greater than or equal to about 0° F. and less than or equal to about170° F.; alternatively, greater than or equal to about 0° F. and lessthan or equal to about 120° F.

For a given temperature, the liquid components (e.g., individuallyand/or in combination) of the liquid phase of the polymerization productmay comprise a pressure at which bubbles begin to form (e.g., thepressure at which the liquid begins to vaporize), referred to herein asthe “bubble point pressure.” The liquid phase of the polymerizationproduct, before being withdrawn and/or discharged from thepolymerization reactor 110, is the liquid phase of the reaction slurryinside the polymerization reactor 110. During polymerization in thereactor 110, the reactor 110 may operate at a pressure such that theliquid phase (e.g., comprising liquids of diluent, monomer, comonomer,or combinations thereof) of the reactor slurry circulating in thereactor 110 has a pressure greater than the bubble point pressure of theliquid at the operating temperature of the reactor 110, in order toavoid bubbles forming in the reactor slurry, which can cause cavitationof the motive device (e.g., pump 150) and/or a serve as a barrier tocirculation of the reactor slurry within the polymerization reactor 110.When the polymerization product is withdrawn and/or discharged (e.g., asa polymerization product slurry) from the reactor 110 (e.g., through theCTO valve 122), separation of the solid phase from the liquid phase isdesired. In an embodiment, the liquid phase is separated from the solidphase via vaporization of one or more liquid components in the liquidphase in the first line 120 (e.g., comprising the CTO valve 122), secondline 130 (e.g., comprising the flashline heater 132), or both. Tofacilitate vaporization the pressure of the polymerization product maybe reduced below the operating pressure in the reactor 110. For example,a drop in pressure may be provided in the first line 120, and thepressure of the polymerization product may be reduced via the drop inpressure which is associated with the CTO valve 122 of the first line120.

In an embodiment, the polymerization product (e.g., polymerizationproduct slurry or product mixture) may be conveyed through the firstline 120, the second line 130, or both, and subjected to a drop inpressure (e.g., via the CTO valve 122) such that the pressure of thepolymerization product is reduced to below the bubble point pressure ofone or more components of the liquid phase (e.g., in the slurry and/orin the mixture) at least at one location in the first line 120, thesecond line 130, or both. In an embodiment, the polymerization product(e.g., polymerization product slurry or product mixture) may besubjected to a drop in pressure (e.g., via the CTO valve 122) such thatthe pressure of the polymerization product is reduced to below thebubble point pressure of a component of the liquid phase, where thecomponent comprises the diluent. In an additional or alternativeembodiment, the polymerization product (e.g., polymerization productslurry or product mixture) may be subjected to a drop in pressure (e.g.,via the CTO valve 122) such that the pressure of the polymerizationproduct is reduced to below the bubble point pressure of a component ofthe liquid phase, where the component comprises the comonomer (e.g.,unreacted). In an additional or alternative embodiment, thepolymerization product (e.g., polymerization product slurry or productmixture) may be subjected to a drop in pressure (e.g., via the CTO valve122) such that the pressure of the polymerization product is reduced tobelow the bubble point pressure of a component of the liquid phase,where the component comprises the monomer (e.g., unreacted). In anadditional or alternative embodiment, the polymerization product (e.g.,polymerization product slurry or product mixture) may be subjected to adrop in pressure (e.g., via the CTO valve 122) such that the pressure ofthe polymerization product is reduced to below the bubble point pressureof a component of the liquid phase, where the component compriseshydrogen.

In an embodiment, the at least one location in the first line 120,second line 130, both, is downstream of the drop in pressure (e.g.,associated with the CTO valve 122 in the first line 120). For example,the location may be in line 126, the flashline heater 132, line 134, theseparation vessel 140, or combinations thereof. In an additional oralternative embodiment, the at least one location of the first line 120,second line 130, or both, is downstream of the CTO valve 122. Forexample, a location may be in line 126, the flashline heater 132, line134, or the separation vessel 140. In an additional or alternativeembodiment, the at least one location of the first line 120, second line130, or both, is upstream of a heat zone of the flashline heater 132.For example, a location may be in the CTO valve 122, in line 126, insecond line 130 upstream of the heat zone (heat zone is described inmore detail below), or in the flashline heater 132 upstream of a heatzone.

In embodiments, the drop(s) in pressure of the first and second lines120 and 130 may vaporize the liquid phase conveyed through the firstline 120 and/or second line 130. In embodiments, the drop in pressure ofthe first line 120 (e.g., associated with CTO valve 122), the drop inpressure of the second line 130 (e.g., associated with the flashlineheater 132), the heating of the second line 130 (e.g., heating of aportion(s) the flashline heater 132), or combinations thereof mayvaporize a substantial amount (e.g., at least about 50%, 75%, 90%, 95%,99%, 99.5%, 99.9%, 99.99%, 99.999%, or 100% by weight of component) ofthe liquid phase in the polymerization product (e.g., polymerizationproduct slurry or mixture) prior to delivery to the separation vessel140. In an embodiment, the drop in pressure of the first line 120 (e.g.,associated with the CTO valve 122), the drop in pressure of the secondline 130 (e.g., associated with the flashline heater 132), the heatingof the second line 130 (e.g., heating of a portion(s) the flashlineheater 132), or combinations thereof may vaporize at least about 50%,75%, 90%, 95%, 99%, 99.5%, 99.9%, 99.99%, 99.999%, or 100% by weight ofcomponent of the liquid phase, where the component is the diluent. Inadditional or alternative embodiment, the drop in pressure of the firstline 120 (e.g., associated with the CTO valve 122), the drop in pressureof the second line 130 (e.g., associated with the flashline heater 132),the heating of the second line 130 (e.g., heating of a portion(s) theflashline heater 132), or combinations thereof may vaporize at leastabout 50%, 75%, 90%, 95%, 99%, 99.5%, 99.9%, 99.99%, 99.999%, or 100% byweight of component of the liquid phase, where the component is thecomonomer (e.g., unreacted). In additional or alternative embodiment,the drop in pressure of the first line 120 (e.g., associated with theCTO valve 122), the drop in pressure of the second line 130 (e.g.,associated with the flashline heater 132), the heating of the secondline 130 (e.g., heating of a portion(s) the flashline heater 132), orcombinations thereof may vaporize at least about 50%, 75%, 90%, 95%,99%, 99.5%, 99.9%, 99.99%, 99.999%, or 100% by weight of component ofthe liquid phase, where the component is the monomer (e.g., unreacted).In additional or alternative embodiment, the drop in pressure of thefirst line 120 (e.g., associated with the CTO valve 122), the drop inpressure of the second line 130 (e.g., associated with the flashlineheater 132), the heating of the second line 130 (e.g., heating of aportion(s) the flashline heater 132), or combinations thereof mayvaporize at least about 50%, 75%, 90%, 95%, 99%, 99.5%, 99.9%, 99.99%,99.999%, or 100% by weight of component of the liquid phase, where thecomponent is hydrogen.

In an embodiment, the drop in pressure associated with the CTO valve 122may vaporize or facilitate vaporization of at least about 10%, 20%, 30%40%, 50%, 75%, 90%, 95%, 99%, 99.5%, 99.9%, 99.99%, 99.999%, or 100% byweight of a component of the liquid phase, where the component comprisesdiluent. In additional or alternative embodiment, the drop in pressureassociated with the CTO valve 122 may vaporize or facilitatevaporization of at least about 10%, 20%, 30% 40%, 50%, 75%, 90%, 95%,99%, 99.5%, 99.9%, 99.99%, 99.999%, or 100% by weight of a component ofthe liquid phase, where the component comprises comonomer (e.g.,unreacted). In additional or alternative embodiment, the drop inpressure associated with the CTO valve 122 may vaporize or facilitatevaporization of at least about 10%, 20%, 30% 40%, 50%, 75%, 90%, 95%,99%, 99.5%, 99.9%, 99.99%, 99.999%, or 100% by weight of a component ofthe liquid phase, where the component comprises hydrogen. In additionalor alternative embodiment, the drop in pressure associated with the CTOvalve 122 may vaporize or facilitate vaporization of at least about 10%,20%, 30% 40%, 50%, 75%, 90%, 95%, 99%, 99.5%, 99.9%, 99.99%, 99.999%, or100% by weight of a component of the liquid phase, where the componentcomprises monomer (e.g., unreacted).

In an embodiment, polymerization product in the first line 120, secondline 130, or both, may be heated to vaporize the liquid phase of thepolymerization product during conveyance therethrough. For example, theflashline heater 132 (as described herein) of the second line 130 mayheat the polymerization product conveyed through the second line 130 tovaporize at least a portion of the liquid phase of the polymerizationproduct.

In embodiments, the average velocity in the first line 120 and/or secondline 130 may be in a range of about 25 ft/s (about 7.6 m/s) to about 270ft/s (about 82.4 m/s); alternatively, in a range of about 40 ft/s (about12.2 m/s) to about 160 ft/s (about 48.8 m/s). In an embodiment, thevelocity of the polymerization product may be below a sonic velocity ofthe polymerization product. In embodiments, the velocity of thepolymerization product through the first line 120 is different than thevelocity of the polymerization product through the second line 130. Inembodiments, the polymerization product may experience more than onevelocity (e.g., before, through, and after the CTO valve 122) as thepolymerization product transfers through the first line 120. Inembodiments, the polymerization product may experience more than onevelocity (e.g., different velocities for one or more segments of aflashline heater 132) as the polymerization product transfers throughthe second line 130.

In an embodiment, the CTO valve 122 may comprise a solids-tolerantvalve. In an additional or alternative embodiment, the CTO valve 122 maycomprise a plug valve, or a ball valve, such as a Vee-Ball valve. In anembodiment, the CTO valve 122 may comprise one or more valves.

In an embodiment, the CTO valve 122 may comprise a nominal diameter ofabout 1 inch to about 8 inches. In embodiments, the nominal diameter ofthe CTO valve 122 may be large enough that the drop in pressureassociated with the CTO valve 122 reduces the pressure of thepolymerization product passing therethrough to a pressure below thebubble point pressure of the liquid phase of the polymerization product.

In an embodiment, the nominal diameter of the CTO valve 122 may be largeenough that the drop in pressure associated with the CTO valve 122reduces the pressure of the polymerization product passing therethroughto a pressure below the bubble point pressure of the liquid phase of thepolymerization product, while accounting for the back pressure in theCTO valve 122, the first line 120, the second line 130, the separationvessel 140, or combinations thereof. For example, the nominal diameterof the CTO valve 122 may be determined relative to the back pressure inthe system 100 in order to reduce the pressure of the polymerizationproduct to a pressure below the bubble point pressure of the liquidphase at a location in the first line 120, second line 130, or both.

As shown in FIG. 1, the flashline heater 132 may comprise a plurality ofsegments 234 connected in series. One or more of the plurality ofsegments 234 of the flashline heater 132 may comprise a segment set. Forexample, flashline heater 132 may have multiple segments, where a firstsegment set 236 comprises segments 234 (e.g., three segments which, forexample, are not heated), a second segment set 237 comprises segments234 (e.g., three segments which, for example, are heated), a thirdsegment set 238 comprises segments 234 (e.g., three segments which, forexample, are not heated), and a fourth segment set 239 comprisessegments 234 (e.g., three segments, for example, which are heated).

In embodiments, a heat zone may comprise a zone of the flashline heater132 which is heated. For example, the heat zone may comprise a portionof a segment 234, a segment 234, or a collection of segments (e.g.,segment set 236, 237, 238, 239, or combinations thereof) which is/areheated as disclosed herein or heated by other means recognized in theart with the aid of this disclosure.

In embodiments, a segment set may comprise a group of the segments 234of the flashline heater 132 which are connected in series and which mayshare a common parameter such as inner diameter, outer diameter, segmentlength, segment material, whether the segments are heated, orcombinations thereof; alternatively, a single segment of the pluralityof segments 234 may comprise a segment set which has a parameterdifferent than other segments and/or segment sets. In other embodiments,segments in a segment set share a common parameter comprising innerdiameter only; alternatively, outer diameter only, alternatively,segment length only.

The flashline heater 132 may be generally sized and configured toreceive polymerization product from the first line 130 (e.g., from theCTO valve 122) and vaporize at least a portion of the liquid phase ofthe mixture flowing into the flashline heater 132, to convert thepolymerization product to a gas phase mixture comprising polymer solidsand a vapor phase of substantially all of the liquid phase.

In an embodiment, a liquid phase of the polymerization product maycomprise a first portion not entrained within solid polymer and a secondportion entrained within the solid polymer. In embodiments, theflashline heater 132 may vaporize substantially all (e.g., at leastabout 99%, 99.9%, 99.99%, 99.999%, or 100% by weight of liquid) of thefirst portion of the liquid phase (i.e., the portion not entrainedwithin the solid polymer) in the polymerization product prior todelivery to the separation vessel 140. In embodiments, the flashlineheater 132 may vaporize a substantial amount (e.g., at least about 75%,90%, 95%, 99%, 99.5% or more by weight of entrained liquid) of thesecond portion of the liquid phase (i.e., the portion entrained withinthe solid polymer) in the polymerization product prior to delivery tothe separation vessel 140.

Generally, the flashline heater 132 may be configured such that thetravel time of the solid polymer through the flashline heater 132 is atleast or greater than about 7.5 seconds; alternatively, greater thanabout 8 second; alternatively, greater than about 8.5 seconds;alternatively, greater than about 9 seconds; alternatively, greater thanabout 9.5 seconds; alternatively, greater than about 10 seconds;alternatively, greater than about 10.5 seconds; alternatively, greaterthan about 11 seconds. In embodiments, the flashline heater 132 may beconfigured such that the travel time of the solid polymer through theflashline heater 132 is about 7.5, 8, 8.5, 9, 9.5, 10, 10.5, 11, 11.5,or more seconds. As the polymerization product flows through theflashline heater 132, the temperature of its various components mayapproach equilibration. For example, the temperature between thevaporized first portion of the liquid, the solid polymer, and the secondportion of the liquid may become substantially equilibrated or have atemperature difference of less than about 10° F.

Generally, at least one of the segments 234 may have an inner diametergreater than an inner diameter of a preceding segment. In an embodiment,at least one of the segments 234 may have an inner diameter greater thana diameter of the CTO valve 122. The inner diameters of the segments 234may increase along the length of the flashline heater 132 as shown inFIG. 1. For example, segments 234 of segment set 237 have an innerdiameter greater than preceding segments 234 of segment set 236,segments 234 of segment set 238 have an inner diameter greater thanpreceding segments 234 of segment sets 237 and 236, and segments 234 ofsegment set 239 have an inner diameter greater than preceding segments234 of segment sets 238, 237, and 236.

In embodiments, the flashline heater 132 may have an inner diameter ofabout 2 inches to about 10 inches. In embodiments, the segments 234 mayhave an inner diameter of about 2 inches to about 10 inches. Inembodiments, each of the segments 234 may have an outer diameter betweenabout 4 and about 16 inches (e.g., about 4 inches, 5 inches, 6 inches, 7inches, 8 inches, inches, 9 inches, 10 inches, 11 inches, 12 inches, 13inches, 14 inches, 15 inches, or 16 inches).

In embodiments, the segments 234 may each have a length that is betweenabout 5 feet and about 100 feet (e.g., about 10 feet, 15 feet, 20 feet,25 feet, 30 feet, 35 feet, 40 feet or greater). Each of segments 234 mayhave the same or different length as other segments, and the length ofeach segment 234 may depend on the particular number of segments 234employed and the total length of the flashline heater 132 in a givenimplementation. In embodiments, the flashline heater 132 may have atotal length greater than about 100 feet; alternatively, greater thanabout 100 feet; alternatively, greater than about 300 feet;alternatively, greater than about 400 feet; alternatively, greater thanabout 500 feet; alternatively, greater than about 600 feet;alternatively, greater than about 700. In an embodiment, the flashlineheater 132 may have a total length of about 560 feet; alternatively,about 630 feet; alternatively, about 700 feet.

In embodiments, the flashline heater 132 may have a length and one ormore inner diameters such that the flashline heater 132 provides thepolymerization product (e.g., polymerization product slurry, productmixture, or combinations thereof) a residence time of at least orgreater than about 7.5; alternatively, greater than about 8 second;alternatively, greater than about 8.5 seconds; alternatively, greaterthan about 9 seconds; alternatively, greater than about 9.5 seconds;alternatively, greater than about 10 seconds; alternatively, greaterthan about 10.5 seconds; alternatively, greater than about 11 seconds.In embodiments, the flashline heater 132 may have a length and one ormore inner diameters such that the flashline heater 132 provides thepolymerization product a residence time of about 7.5, 8, 8.5, 9, 9.5,10, 10.5, 11, 11.5, or more seconds.

The separation vessel 140 may recover solid polymer which is receivedfrom the second line 130. In one or more of the embodiments disclosedherein, the polymerization product flowing from the second line 130 (forexample, a mixture of solid polymer and at least a portion,substantially all or all of the other components, e.g., diluent and/orunreacted monomer/comonomer, are in a gas phase) may be separated intosolid polymer in line 144 and one or more gases in line 142 inseparation vessel 140.

Any suitable technique may be used to separate the polymerizationproduct to recover solid polymer. For example, the separation vessel 140may comprise a vapor-liquid separator. Suitable embodiments of avapor-liquid separator may include a distillation column, a flash tank,a filter, a membrane, a reactor, an absorbent, an adsorbent, a molecularsieve, a cyclone, or combinations thereof. In an embodiment, theseparator comprises a flash tank. Not seeking to be bound by theory,such a flash tank may comprise a vessel configured to vaporize and/orremove low vapor pressure components from a high temperature and/or highpressure fluid.

In an embodiment, the separation vessel 140 may be configured such thatpolymerization product from second line 130 may be separated into solidphase and liquid (e.g., a condensate) phase components in line 144 and agas (e.g., vapor) phase components in line 142. The solid phase maycomprise solid polymer (e.g., polyethylene, optionally, a polyethylenecopolymer). The liquid phase or condensate may comprise any liquid phasecomponents such as diluent and/or unreacted monomer/comonomer. In someembodiments, line 144 comprises a concentrated slurry of the solid phaseand liquid phase in comparison to the product slurry in lines 120 and130. The gas or vapor phase may comprise vaporized solvents, diluent,unreacted monomers and/or optional unreacted comonomers, waste gases(e.g., secondary reaction products, such as contaminants and the like),or combinations thereof. The separations vessel 140 may be configuredsuch that the polymerization product flowing in the second line 130 isflashed by heat, pressure reduction, or combinations thereof such thatthe enthalpy of the line is increased. This may be accomplished via aheater (e.g., a flashline heater 132). For example, a flashline heatercomprising a double pipe may exchange heat by hot water or steam may beutilized.

In an alternative embodiment, the separation vessel 140 may beconfigured such that polymerization product from second line 130 may beseparated into solid polymer in line 144 substantially or completelyfree of any liquid phase components, and into one or more gases in line142. Suitable separation techniques include distilling, vaporizing,flashing, filtering, membrane screening, absorbing, adsorbing,cycloning, gravity settling, or combinations thereof, the polymerizationproduct received in separation vessel 140 from the second line 130.

In an embodiment, the separation vessel 140 may operate at a pressure offrom about 50 psig to about 500 psig; alternatively, from about 130 psigto about 190 psig; alternatively, at about 150 psig; alternatively, atabout 135 psig.

In one or more embodiments, the gas in line 142 may comprise hydrogen,nitrogen, methane, ethylene, ethane, propylene, propane, butane,1-butene, isobutane, pentane, hexane, 1-hexene, heavier hydrocarbons, orcombinations thereof. In an embodiment, ethylene may be present in arange of from about 0.1% to about 15%, alternatively, from about 1.5% toabout 5%, alternatively, about 2% to about 4% by total weight of theline. Ethane may be present in a range of from about 0.001% to about 4%,alternatively, from about 0.2% to about 0.5% by total weight of theline. Isobutane may be present in a range from about 80% to about 98%,alternatively, from about 92% to about 96%, alternatively, about 95% bytotal weight of the line.

The separation vessel 140 may additionally comprise any equipmentassociated with the separation vessel 140, such as control devices(e.g., a PID controller) and measurement instruments (e.g.,thermocouples), and level control and measurement devices.

In an embodiment, the horizontal distance between the separation vessel140 and the loop slurry polymerization reactor 110 may be adjusted tooptimize layout and cost. In an embodiment, the separation vessel 140which may be from about 0 to about 3,000 horizontal feet from the loopslurry polymerization reactor 110; alternatively, the separation vessel140 may be from about 0 to about 1,500 horizontal feet from the loopslurry polymerization reactor 110; alternatively, the separation vessel140 may be from about 100 to about 1,500 horizontal feet from thereactor 110; alternatively, the separation vessel 140 may be from about100 to about 500 horizontal feet from the reactor 110; alternatively,the separation vessel 140 may be from about 100 to about 500 horizontalfeet from the reactor 110. In various embodiments, the polymerizationproduct may travel a linear distance through first line 120 and second130 in x, y, and z coordinates, for example through circuitous piperouting, that is greater than the horizontal distance, the verticalspacing/distance, or combinations thereof.

In embodiments, the system 100 may further comprise a control system 160for controlling the withdrawal of polymerization product from the loopslurry polymerization reactor 110. The control system 160 may control,for example, the CTO valve 122 and/or control and/or measurementinstruments for the loop slurry polymerization reactor 120 (e.g.,sensors of weight percent solids, reactor pressure, supply of feed,fluidized bed height, etc., or combinations thereof). The control system160 may additionally or alternatively monitor and maintain the amount ofpolymerization product in the loop slurry polymerization reactor 110 bycontrolling the flow of polymerization product from the reactor 110 tothe separation vessel 160 via the first line 120 and second line 130.The control system 160 may additionally or alternatively monitor lineconditions with sensors 146, e.g., for lines 134, 142, and 144. Thecontrol system 160 may additionally or alternatively monitor andmaintain the level of solid polymer in the separation vessel 140, forexample via one or more sensors 146. The control system 160 mayadditionally or alternatively control a heating of the flashline heater132. In an embodiment, the control system 160 may adjust a flow ofpolymerization product in the first line 120 and/or second line 130 viaadjustment of the CTO valve 122.

FIG. 2 shows a cross-sectional view of an embodiment of a portion of theflashline heater 132, taken along sight line 2-2 of FIG. 1. The portionof the flashline heater 132 has length “l”. As shown in FIG. 2, apolymerization product may enter the portion of the flashline heater 132in the direction of arrow 222. At least a portion of the liquidcomponents in polymerization product may convert to gas phase, therebyyielding a mixture in line 134 (e.g., polymer solids, gas phasecomponents, and in some instances, remaining liquid phase components)which exits the portion of the flashline heater 132. In embodiments,substantially all the liquid phase components in the polymerizationproduct may convert to gas phase, thereby yielding a gas phase productmixture in line 134. The characteristics (e.g., amount of gas and/orliquid phase of various components) of the product stream 134 deliveredto the separation vessel 140 may depend on many factors including butnot limited to a length “l.” of the portion of the flashline heater 132,a diameter “d_(o)” of an outer conduit 270 of the flashline heater 132,an internal diameter “d_(i)” of the segments 234 of the flashline heater132, the velocity of the product stream in the flashline heater 132, thevelocity of the polymerization product in the flashline heater 132 inrelation to the take-off velocity of the polymerization product, thechemical nature of the components within the polymerization product, thedrop in pressure occurring upstream from the flashline heater 132 (e.g.,in CTO valve 122), or combinations thereof.

To affect the vaporization of the liquid phase within the polymerizationproduct, the flashline heater 132 may also include a plurality ofsegments 235 forming an outer conduit 270, which may wrap around atleast a portion of one or more of the segments 234. The segments 235 maybe configured to facilitate a flow of a warming medium through a portionor the entire outer conduit 270. The segments 235 may have the same ordiffering diameters and/or lengths as one another. In embodiments, thesegments 235 may have correspondingly same or differing diameters and/orlengths as the segments 234 which they wrap around.

In an embodiment, the warming medium that flows through the segments 235may allow the flashline heater 132 to heat the polymerization product inone or more heat zones, for example, length l, one or more sections(e.g., segment sets—contiguous or non-contiguous) of the flashlineheater 132, or throughout the entire length of the flashline heater 132.That is, the segments 235 of the flashline heater 132 may increase,decrease, or maintain the temperature of the polymerization product asit flows through segments 234, which may allow for control of theheating rate and/or resulting temperature of the solid polymer as thepolymerization product flows through the flashline heater 132, asportions of the liquid components of the polymerization product convertto gas phase, as the mixed phase product stream 134 exits the flashline132, or combinations thereof. During operation, the warming medium mayflow through one or more segments 235 of the outer conduit 270, whichindirectly heats the polymerization product as the polymerizationproduct flows through the segments 234. In other words, the warmingmedium flowing through one segment 235 may be substantially separatedfrom the warming medium flowing through another segment 235, such thateach segment 235 may be separated from the other, thereby allowingindependent control of heating across one or more segments.Alternatively or additionally, two or more segments 235 may share a flowof warming medium. For example, the two or more segments 235 may share asingle inlet and outlet. In some embodiments, the warming medium may bewarmed coolant from the cooling jackets of the polymerization reactor(e.g., jackets 113 of FIG. 1), steam or steam condensate, hot oil,another heating source such as heat generated by electrical resistanceheaters, or combinations thereof.

In embodiments, the flashline heater 132 may allow warming medium toflow through any one or a combination of the segments 235. For example,the heating medium may flow through a first set 206 of segments 235 butnot through a second set 208 of segments 235, or any similar flow ortemperature scheme, such as through every third segment, or throughthree segments and not through a fourth, and so on. For example, in theillustrated embodiment, the warming medium may flow into a respectiveinlet 210 and out of a respective outlet 212 of each one of the segments235. Alternatively, combinations of segments 235 may have a common inletand/or a common outlet. In one implementation, when the warming mediumflows through the first set 206 of segments 235 but not the second set208, it may initially warm the polymerization product such thatsubstantially all of the liquid within the polymerization product isvaporized, followed by a period of cooling or temperature maintenance.Whether the second set 208 of segments 235 may be used to provide heatmay depend on the measured levels of liquid (e.g., diluent) entrainedwithin the solid polymer, the desired specifications of the solidpolymer, desired solid polymer temperature, or combinations thereof.However, it should be noted that, in embodiments where the flashlineheater 132 is configured to substantially continuously heat thepolymerization product along a length of greater than about 700 feet,the solid polymer may begin to melt, which may cause difficulty infurther processing. By controlling the amount of warming fluid flowingthrough each segment 235 or combination of segment sets (such as 206 and208), an operator and/or controller may be able to adjust thetemperature of the polymerization product to a desired level. In oneembodiment, the temperature difference between the vapor and solidpolymer in the mixed phase product stream 134 exiting the flashlineheater 132 may be substantially negligible or the temperature of thesolid polymer may approach about within 40° F., 20° F., 10° F., 5° F.,or 1° F. of the temperature of the vapor. Further, the mixed phaseproduct stream 134 may approach a thermal equilibrium, such thatsubstantially all of the liquid present (e.g., liquid entrained in thesolid polymer), the vapor and the solid polymer each have a temperaturethat differ from one another by no more than 1° F.

In an embodiment, the flashline heater 132 may reduce a boiling point ofliquid in the polymerization product at a given pressure. In such anembodiment, the liquid may more readily vaporize in the flashline heater132.

In additional or alternative embodiments, the vaporization and/orthermal equilibration may at least partially depend on the total lengthof the flashline heater 132. For example, the total length of theflashline heater 132 may at least partially determine the temperature ofthe product stream 134 as well as the extent of entrained liquidremaining within the solid polymer. In a general sense, the total lengthof the flashline heater 132 may at least partially determine how muchtime the polymerization product may spend in heated areas, in cooledareas, in areas of high and/or low pressure, and so on. In this way, thetotal length of the flashline heater 132 may at least partiallydetermine the amount of time between full vaporization of liquids notassociated or entrained within the solid polymer of the polymerizationproduct and the delivery of the product stream 134 exiting the flashlineheater to the separation vessel 140. Therefore, it should be noted thatin some configurations, such as those with a substantially constantdiameter and temperature, that as the total length of the flashlineheater 132 increases, so may the transit time of the polymerizationproduct through the flashline heater 132 and the likelihood that thefirst portion of the liquid phase is completely vaporized and the secondportion of the liquid phase has been substantially vaporized (asdescribed above).

While the total length of the flashline heater 132 may at leastpartially determine the transit time of the polymerization product, thediameters d_(i) and d_(o) may at least partially determine the rate atwhich the liquid phase within the polymerization product vaporizes.Therefore, the total length and diameters d_(i) and d_(o) of theflashline heater 132 may have a synergistic effect in determining thecharacteristics of the product stream 134 exiting the flashline heaterand delivered to the separation vessel 140. Therefore, it should benoted that an increase in both the total length and the internaldiameter d_(i) relative to conventional dimensions may greatly increasethe probability of full vaporization of liquids and/or temperatureequilibration for the vapor, liquids, solid polymer, or combinationsthereof.

In embodiments, the inner diameter d_(i) of segments 234 may changealong the length of the flashline heater 132. Therefore, thepolymerization product may experience changing pressure proportional tothe diameter change as it progresses through the flashline heater 132.Temperature and/or pressure changes may be substantially static (e.g.,unchanging throughout the total length of the flashline heater 132 intime) or may be dynamic (e.g., changing throughout the total length ofthe flashline heater 132 in time). That is, the segments 234 may havedifferent or the same heating temperatures, different or the samepressures, or combinations thereof.

To reach substantial vaporization and/or thermal equilibrium, inaccordance with present embodiments, the polymerization product may flowthrough the flashline heater 132 through the segments 234 havinginternal diameter d_(i). Substantially concurrently, the polymerizationproduct is heated by a warming fluid within the outer conduit 270 havingthe diameter d_(o), which may surrounds at least a portion of one ormore of segments 234. According to the present approaches, either orboth of these diameters may impact the rate at which liquids within thepolymerization product vaporize. For example, in some embodiments, theinner diameter d_(i) may be inversely proportional to the pressurewithin the flashline heater 132. That is, as the diameter d_(i)increases, the pressure acting on the polymerization product maydecrease, which may allow an increased rate of vaporization of theliquids. Also, as the d_(i) increases, the velocity decreases andprovides additional residence time for vaporization. Accordingly, insome embodiments, the internal diameter d_(i) of the segments 234 isincreased relative to conventional designs, such as to diameters of atleast 2, 3, 4, 5, 6, 7, or 8 inches, or more.

An increase in the diameter d_(o) may also increase the rate ofvaporization of the liquids within the polymerization product. Forexample, the diameter d_(o) may define the amount of warming fluidavailable to the outer surface of the segments 234 for indirectlyheating the polymerization product. While the exchange of heat betweenthe warming medium and the polymerization product may be substantiallylimited by the outer and inner surface areas of the segments 234, itshould be noted that as the diameter d_(o) of the outer conduit 270increases, so may the amount of warming medium available for heatexchange. Accordingly, as the amount of warming medium within the outerconduit 270 increases, heat transfer to the polymerization product mayhave a minimized impact on the average temperature of the warming mediumwithin the outer conduit 270. Therefore, by increasing the diameterd_(o) relative to diameter d_(i), more efficient heating of thepolymerization product, and therefore vaporization of the liquids withinthe polymerization product, may be realized.

It should be noted, in light of the present discussion, that thediameter d_(o) of the outer conduit 270, the diameter d_(i) of one ormore segments 234, the total length of the flashline heater 132, andtheir interrelation may at least partially determine the relative timesof conversion for the liquid(s) of the polymerization product enteringthe flashline heater to convert to vapor in product stream 134 exitingthe flashline heater 132.

Embodiments of the disclosure include processes for making a low densitypolymer in a polymerization reactor, for example, utilized by the system100 of FIG. 1.

In an embodiment, a process comprises polymerizing an olefin monomer,and optionally an olefin comonomer, in the presence of a diluent in apolymerization reactor 110 to make a polymerization product slurryconsisting of a liquid phase and a solid phase, wherein the solid phasecomprises an olefin polymer having a density of between about 0.905g/cm³ to about 0.945 g/cm³; and discharging the polymerization productslurry from the polymerization reactor through a continuous take-offvalve 122 to make a mixture further comprising a vapor phase. Theprocess may further comprise conveying the mixture downstream of thecontinuous take-off valve 122 at a temperature less than a meltingtemperature of the olefin polymer. The mixture may comprise a pressureless than a bubble point pressure of a component in the polymerizationproduct slurry. In an embodiment, the component may comprise thediluent. In an additional or alternative embodiment, the component maycomprise the comonomer. In an embodiment, a location of the mixture isdownstream of the continuous take-off valve 122. In an additional oralternative embodiment, the location of the mixture is upstream of aheat zone in a flashline heater 132. In an embodiment, the vapor phasemay comprise ethylene, isobutane, ethane, hydrogen, or combinationsthereof. In an additional or alternative embodiment, the vapor phase maycomprise a vaporized portion of the liquid phase. In an embodiment, theliquid phase may comprise the diluent, the monomer, a comonomer, orcombinations thereof. In an embodiment, the diluent may compriseisobutane. In an additional or alternative embodiment, the monomer maycomprise ethylene. In an additional or alternative embodiment, thecomonomer may comprise propylene, 1-butene, 1-hexene, 1-octene, orcombinations thereof. In an embodiment, the olefin polymer comprisespolyethylene. In an additional or alternative embodiment, the olefinpolymer further comprises a copolymer. In an additional or alternativeembodiment, the olefin polymer comprises a linear low-densitypolyethylene. In an embodiment, the continuous take-off valve has anominal diameter of about 1 inch to about 8 inches.

Embodiments of the disclosure include processes for pressure managementof a polymerization product in slurry polymerization, for example,utilized by the system 100 of FIG. 1.

In an embodiment, a process comprises conveying the polymerizationproduct slurry through a continuous take-off valve 122, wherein thepolymerization product slurry comprises a liquid phase and a solidphase, converting the polymerization product slurry to a mixture,wherein the mixture comprises at least a portion of the liquid phase,the solid phase, and a vapor phase, and conveying the mixture through aflashline heater 132, wherein, at least at one location downstream ofthe continuous take-off valve, the mixture comprises a pressure lessthan a bubble point pressure of the liquid phase. In an embodiment, theprocess further includes conveying the mixture through the flashlineheater 132 at a temperature less than a melting temperature of the solidpolymer. In an embodiment, the liquid phase comprises a diluent,unreacted monomer, unreacted comonomers, or combinations thereof. In anembodiment, the diluent comprises isobutane, wherein the unreactedmonomer comprises ethylene, wherein the unreacted comonomer comprisespropylene, 1-butene, 1-hexene, 1-octene, or combinations thereof. In anembodiment, the vapor phase comprises a vaporized portion of the liquidphase. In an embodiment, the solid phase comprises a solid polymer. Inan embodiment, the solid polymer comprises polyethylene. In anembodiment, the solid polymer further comprises a polyethylenecopolymer. In an embodiment, the polyethylene comprises a density in therange of about 0.905 g/cm³ to about 0.945 g/cm³. In an embodiment, thepolyethylene comprises a linear low-density polyethylene. In anembodiment, the continuous take-off valve 122 has a nominal diameter ofabout 1 inch to about 8 inches.

In embodiments where a low-density solid polymer is produced in thereactor 110, operating temperatures are generally lower than inembodiments where a high-density solid polymer is produced (e.g., toavoid swelling, softening, melting of the solid polymer in the reactor110 which fouls the reactor 110). The lower temperature of the reactor110 translates into a lower temperature which can be heated to in theflashline heater 132, in order to avoid swelling, softening, melting, orcombinations thereof of the solid polymer in the flashline heater 132.As such, the drop in pressure associated with the CTO valve 122 belowthe bubble point pressure of one or more components of the liquid phaseof the polymerization product facilitates vaporization of the liquidphase of the polymerization product in the system 100. Vaporization ofthe liquid phase which would otherwise not be vaporized reduces theamounts of liquid which reach the separation vessel 140, thus reducingthe load on the separation vessel 140, other equipment downstream, inany recycle lines, or combinations thereof. The drop in pressure to apressure below the bubble point pressure of a component in the liquidphase in the polymerization product may also provide a cooling effectwhich avoids swelling, softening, melting, or combinations thereof ofthe solid polymer as the polymerization product passes through the firstline 120, the second line 130, or both. Managing the pressure of thepolymerization product to below the bubble point pressure of one or morecomponents of the liquid phase may also increase a production capacityfor a given slurry polymerization system.

EXAMPLES

The disclosure having been generally described, the following propheticor hypothetical examples are given as particular embodiments of thedisclosure and to demonstrate the expected practice and advantagesthereof. It is understood that these examples are given by way ofillustration and is not intended to limit the specification or theclaims in any manner.

PROPHETIC EXAMPLE Embodiment 1

Ethylene is polymerized to form polyethylene in one or more loop slurrypolymerization reactors, such as reactor 110 in FIG. 1. The operatingtemperature of the reactor 110 is from about 60° C. to about 280° C. Theoperating pressure of the reactor 110 is about 650 psig. The monomer isethylene. The diluent in the reactor 110 is isobutane, and the catalystsystem is one of the catalyst systems described hereinabove. Theisobutane, ethylene, and catalyst system are moved through the reactor110 as a reactor slurry, for example, via motive device 150, where theethylene and isobutane are in liquid phase, the catalyst system is inliquid and/or solid phase, and polyethylene formed by the polymerizationreaction is in the solid phase. The operating pressure of the reactor110 is above the bubble point pressure of the isobutane and theethylene.

The reactor slurry is withdrawn and/or discharged from the reactor 110as a polymerization product slurry comprising ethylene (e.g., unreacted,if any), isobutane, and polyethylene. The withdrawn polymerizationproduct slurry is discharged through the CTO valve 122 such that thepolymerization product slurry experiences a drop in pressure to apressure below 650 psig, the operating pressure of the reactor 110. Thedrop in pressure facilitates vaporization of at least a portion of theliquid phase of the polymerization product slurry to yield a mixture.Additionally, the polymerization product slurry experiences a drop inpressure to a pressure below the bubble point pressure of ethylene, ofisobutane, or both.

If the drop in pressure is to a pressure below the bubble point pressureof ethylene, then at least a portion of the ethylene in the liquid phasevaporizes as the mixture is conveyed downstream of the CTO valve 122. Ifthe drop in pressure is to a pressure below the bubble point pressure ofisobutane then at least a portion of the isobutane in the liquid phasevaporizes as the mixture is conveyed downstream of the CTO valve 122. Ifthe drop in pressure is to a pressure below the bubble point pressure ofethylene and isobutane then at least a portion of the ethylene andisobutane in the liquid phase vaporizes as the mixture is conveyeddownstream of the CTO valve 122.

The pressure which is below the bubble point pressure facilitatesvaporization of the liquid phase of the polymerization product slurryand mixture, for example, in the production of linear low densitypolyethylene which requires lower operating pressures in thepolymerization reactor 110.

PROPHETIC EXAMPLE Embodiment 2

Ethylene and 1-hexene are polymerized to form polyethylene and copolymerin one or more loop slurry polymerization reactors, such as reactor 110in FIG. 1. The operating temperature of the reactor 110 is from about60° C. to about 280° C. The operating pressure of the reactor 110 isabout 650 psig. The monomer is ethylene, and the comonomer is 1-hexene.The diluent in the reactor 110 is isobutane, and the catalyst system isone of the catalyst systems described hereinabove. The isobutane,ethylene, 1-hexene, and catalyst system are moved through the reactor110 as a reactor slurry, for example, via motive device 150, where theethylene and isobutane are in liquid phase, the catalyst system is inliquid and/or solid phase, and polyethylene and copolymer formed by thepolymerization reaction is in the solid phase. The operating pressure ofthe reactor 110 is above the bubble point pressure of the isobutane,ethylene, and 1-hexene.

The reactor slurry is withdrawn and/or discharged from the reactor 110as a polymerization product slurry comprising ethylene (e.g., unreacted,if any), 1-hexene (e.g., unreacted, if any), isobutane, polyethylene,and copolymer. The withdrawn polymerization product slurry is dischargedthrough the CTO valve 122 such that the polymerization product slurryexperiences a drop in pressure to a pressure below 650 psig, theoperating pressure of the reactor 110. The drop in pressure facilitatesvaporization of at least a portion of the liquid phase of thepolymerization product slurry to yield a mixture. Additionally, thepolymerization product slurry experiences a drop in pressure to apressure below the bubble point pressure of ethylene, of 1-hexene, ofisobutane, or combinations thereof.

If the drop in pressure is to a pressure below the bubble point pressureof ethylene, then at least a portion of the ethylene in the liquid phasevaporizes as the mixture is conveyed downstream of the CTO valve 122. Ifthe drop in pressure is to a pressure below the bubble point pressure of1-hexene, then at least a portion of the 1-hexene in the liquid phasevaporizes as the mixture is conveyed downstream of the CTO valve 122. Ifthe drop in pressure is to a pressure below the bubble point pressure ofisobutane then at least a portion of the isobutane in the liquid phasevaporizes as the mixture is conveyed downstream of the CTO valve 122. Ifthe drop in pressure is to a pressure below the bubble point pressure ofethylene and isobutane then at least a portion of the ethylene andisobutane in the liquid phase vaporizes as the mixture is conveyeddownstream of the CTO valve 122. If the drop in pressure is to apressure below the bubble point pressure of ethylene and 1-hexene thenat least a portion of the ethylene and 1-hexene in the liquid phasevaporizes as the mixture is conveyed downstream of the CTO valve 122. Ifthe drop in pressure is to a pressure below the bubble point pressure ofisobutane and 1-hexene then at least a portion of the isobutane and1-hexene in the liquid phase vaporizes as the mixture is conveyeddownstream of the CTO valve 122.

The pressure which is below the bubble point pressure facilitatesvaporization of the liquid phase of the polymerization product slurryand mixture, for example, in the production of linear low densitypolyethylene which requires lower operating pressures in thepolymerization reactor.

ADDITIONAL DESCRIPTION

Processes and systems for the production for pressure management of apolymerization product flowing from a loop polymerization reactor to aseparation vessel in a slurry polymerization system have been described.The following are a first set of nonlimiting, specific embodiments inaccordance with the present disclosure:

Embodiment 1 is a process for making a low density polymer in apolymerization reactor system, the process comprising polymerizing anolefin monomer, and optionally an olefin comonomer, in the presence of adiluent in a polymerization reactor to make a polymerization productslurry consisting of a liquid phase and a solid phase, wherein the solidphase comprises an olefin polymer having a density of between about0.905 g/cm³ to about 0.945 g/cm³; and discharging the polymerizationproduct slurry from the polymerization reactor through a continuoustake-off valve to make a mixture further comprising a vapor phase.

Embodiment 2 is the process of embodiment 1, wherein the mixturecomprises a pressure less than a bubble point pressure of a component inthe polymerization product slurry.

Embodiment 3 is the process of embodiment 2, wherein the component isthe diluent.

Embodiment 4 is the process of embodiment 2, wherein the component isthe comonomer.

Embodiment 5 is the process of one of embodiments 1 to 4, wherein alocation of the mixture is downstream of the continuous take-off valve.

Embodiment 6 is the process of one of embodiments 1 to 5, wherein thelocation of the mixture is upstream of a heat zone in a flashlineheater.

Embodiment 7 is the process of one of embodiments 1 to 6, wherein thevapor phase comprises ethylene, isobutane, ethane, hydrogen, orcombinations thereof.

Embodiment 8 is the process of one of embodiments 1 to 7, wherein thevapor phase comprises a vaporized portion of the liquid phase.

Embodiment 9 is the process of one of embodiments 1 to 8, wherein theliquid phase comprises the diluent, the monomer, the comonomer, orcombinations thereof.

Embodiment 10 is the process of one of embodiments 1 to 9, wherein thediluent comprises isobutane, wherein the monomer comprises ethylene,wherein the comonomer comprises propylene, 1-butene, 1-hexene, 1-octene,or combinations thereof.

Embodiment 11 is the process of one of embodiments 1 to 10, furthercomprising conveying the mixture downstream of the continuous take-offvalve at a temperature less than a melting temperature of the olefinpolymer.

Embodiment 12 is the process of one of embodiments 1 to 11, wherein theolefin polymer comprises polyethylene.

Embodiment 13 is the process of embodiment 12, wherein the olefinpolymer further comprises a copolymer.

Embodiment 14 is the process of one of embodiments 1 to 13, wherein theolefin polymer comprises a linear low-density polyethylene.

Embodiment 15 is the process of one of embodiments 1 to 14, wherein thecontinuous take-off valve has a nominal diameter of about 1 inch toabout 8 inches.

Embodiment 16 is a process for pressure management of a polymerizationproduct slurry withdrawn from a loop polymerization reactor in slurrypolymerization, the process comprising conveying the polymerizationproduct slurry through a continuous take-off valve, wherein thepolymerization product slurry comprises a liquid phase and a solidphase; converting the polymerization product slurry to a mixture,wherein the mixture comprises at least a portion of the liquid phase,the solid phase, and a vapor phase; and conveying the mixture through aflashline heater; wherein, at least at one location downstream of thecontinuous take-off valve, the mixture comprises a pressure less than abubble point pressure of the liquid phase.

Embodiment 17 is the process of embodiment 16, wherein the liquid phasecomprises a diluent, unreacted monomer, unreacted comonomers, orcombinations thereof.

Embodiment 18 is the process of embodiment 17, wherein the diluentcomprises isobutane, wherein the unreacted monomer comprises ethylene,wherein the unreacted comonomer comprises propylene, 1-butene, 1-hexene,1-octene, or combinations thereof.

Embodiment 19 is the process of one of embodiments 16 to 18, wherein thevapor phase comprises a vaporized portion of the liquid phase.

Embodiment 20 is the process of one of embodiments 16 to 19, wherein thesolid phase comprises a solid polymer.

Embodiment 21 is the process of embodiment 20, further comprisingconveying the mixture through the flashline heater at a temperature lessthan a melting temperature of the solid polymer.

Embodiment 22 is the process of one of embodiments 20 to 21, wherein thesolid polymer comprises polyethylene.

Embodiment 23 is the process of embodiment 22, wherein the solid polymerfurther comprises a polyethylene copolymer.

Embodiment 24 is the process of one of embodiments 22 to 23, wherein thepolyethylene comprises a density in the range of about 0.905 g/cm³ toabout 0.945 g/cm³.

Embodiment 25 is the process of one of embodiments 22 to 24, wherein thepolyethylene comprises a linear low-density polyethylene.

Embodiment 26 is the process of one of embodiments 16 to 25, wherein thecontinuous take-off valve has a nominal diameter of about 1 inch toabout 8 inches.

Embodiment 27 is a process for pressure management of a polymerizationproduct in slurry polymerization, the process comprising withdrawing apolymerization product slurry from a loop polymerization reactor,wherein the polymerization product slurry comprises a liquid phase and asolid phase; conveying the polymerization product slurry through a firstline comprising a continuous take-off valve to yield a mixture, whereinthe mixture comprises at least a portion of the liquid phase, the solidphase, and a vapor phase; and conveying the mixture through a secondline comprising a flashline heater; wherein, at least at one location inthe first line, the second line, or both, the mixture comprises apressure less than a bubble point pressure of the liquid phase.

Embodiment 28 is the process of embodiment 27, wherein the at least onelocation in the first line, second line, or both is downstream of thecontinuous take-off valve.

Embodiment 29 is the process of one of embodiments 27 to 28, wherein theat least one location in the first line, second, or both is upstream ofa heat zone in the flashline heater.

Embodiment 30 is the process of one of embodiments 27 to 29, furthercomprising providing a drop in pressure in the first line, wherein theat least one location in the first line, second line, or both isdownstream of the drop in pressure.

Embodiment 31 is the process of embodiment 30, wherein the drop inpressure is associated with the continuous take-off valve.

Embodiment 32 is the process of one of embodiments 27 to 31, wherein theliquid phase comprises a diluent, unreacted monomer, unreactedcomonomer, or combinations thereof.

Embodiment 33 is the process of embodiment 32, wherein the diluentcomprises isobutane, wherein the unreacted monomer comprises ethylene,wherein the unreacted comonomer comprises propylene, 1-butene, 1-hexene,1-octene, or combinations thereof.

Embodiment 34 is the process of one of embodiments 27 to 33, wherein thevapor phase comprises a vaporized portion of the liquid phase.

Embodiment 35 is the process of one of embodiments 27 to 34, wherein thesolid phase comprises a solid polymer.

Embodiment 36 is the process of one of embodiments 27 to 35, furthercomprising conveying the mixture through the second line at atemperature less than a melting temperature of the solid polymer.

Embodiment 37 is the process of one of embodiments 35 to 36, wherein thesolid polymer comprises polyethylene.

Embodiment 38 is the process of embodiment 37, wherein the solid polymerfurther comprises a polyethylene copolymer.

Embodiment 39 is the process of one of embodiments 37 to 38, wherein thepolyethylene comprises a density in the range of about 0.905 g/cm³ toabout 0.945 g/cm³.

Embodiment 40 is the process of one of embodiments 37 to 39, wherein thepolyethylene comprises a linear low-density polyethylene.

Embodiment 41 is the process of one of embodiments 27 to 40, wherein thecontinuous take-off valve has a nominal diameter of about 1 inch toabout 8 inches.

Embodiment 42 is a system for pressure management of a polymerizationproduct in slurry polymerization comprising a loop slurry polymerizationreactor which forms polymerization product, a first line which receivesa polymerization product from the loop slurry polymerization reactor, asecond line which receives the polymerization product from the firstline, and a separation vessel which receives the polymerization productfrom the second line.

Embodiment 43 is the system of embodiment 42, wherein a solid polymer isrecovered from the separation vessel.

Embodiment 44 is the system of one of embodiments 42 to 43, wherein thefirst line comprises a continuous take-off valve.

Embodiment 45 is the system of one of embodiments 42 to 44, wherein thesecond line comprises a flashline heater.

Embodiment 46 is the system of one of embodiments 44 to 45, wherein thecontinuous take-off valve provides a drop in pressure for thepolymerization product conveyed through the first line.

Embodiment 47 is the system of one of embodiments 42 to 46, wherein thepolymerization product comprises a liquid phase, wherein a pressure ofthe polymerization product is below a bubble-point pressure of theliquid phase at least at one location in the first line, the secondline, or both.

Processes and systems for the production for pressure management of apolymerization product flowing from a loop polymerization reactor to aseparation vessel in a slurry polymerization system have been described.

While preferred embodiments of the invention have been shown anddescribed, modifications thereof can be made by one skilled in the artwithout departing from the spirit and teachings of the invention. Theembodiments described herein are exemplary only, and are not intended tobe limiting. Many variations and modifications of the inventiondisclosed herein are possible and are within the scope of the invention.Where numerical ranges or limitations are expressly stated, such expressranges or limitations should be understood to include iterative rangesor limitations of like magnitude falling within the expressly statedranges or limitations (e.g., from about 1 to about 10 includes, 2, 3, 4,etc.; greater than 0.10 includes 0.11, 0.12, 0.13, etc.). Use of theterm “optionally” with respect to any element of a claim is intended tomean that the subject element is required, or alternatively, is notrequired. Both alternatives are intended to be within the scope of theclaim. Use of broader terms such as comprises, includes, having, etc.should be understood to provide support for narrower terms such asconsisting of, consisting essentially of, comprised substantially of,etc.

Accordingly, the scope of protection is not limited by the descriptionset out above but is only limited by the claims which follow, that scopeincluding all equivalents of the subject matter of the claims. Each andevery claim is incorporated into the specification as an embodiment ofthe present invention. Thus, the claims are a further description andare an addition to the preferred embodiments of the present invention.The discussion of a reference in the disclosure is not an admission thatit is prior art to the present invention, especially any reference thatmay have a publication date after the priority date of this application.The disclosures of all patents, patent applications, and publicationscited herein are hereby incorporated by reference, to the extent thatthey provide exemplary, procedural or other details supplementary tothose set forth herein.

What is claimed is:
 1. A process for making a low density polymer in apolymerization reactor system, the process comprising: polymerizing anolefin monomer, and optionally an olefin comonomer, in the presence of adiluent in a polymerization reactor to make a polymerization productslurry consisting of a liquid phase and a solid phase, wherein the solidphase comprises an olefin polymer having a density of between about0.905 g/cm³ to about 0.945 g/cm³; and discharging the polymerizationproduct slurry from the polymerization reactor through a continuoustake-off valve to make a mixture further comprising a vapor phaseupstream of a flashline heater, wherein the flashline heater is upstreamof a separation vessel, wherein the mixture comprises, at least at onelocation upstream of the separation vessel, a pressure less than abubble point pressure of a component in the polymerization productslurry.
 2. The process of claim 1, wherein the component is the diluent.3. The process of claim 1, wherein the component is the comonomer. 4.The process of claim 1, wherein a location of the mixture is downstreamof the continuous take-off valve.
 5. The process of claim 4, wherein thelocation of the mixture is upstream of a heat zone in a flashlineheater.
 6. The process of claim 1, wherein the vapor phase comprisesethylene, isobutane, ethane, hydrogen, or combinations thereof.
 7. Theprocess of claim 1, wherein the vapor phase comprises a vaporizedportion of the liquid phase.
 8. The process of claim 1, wherein theliquid phase comprises the diluent, the monomer, the comonomer, orcombinations thereof.
 9. The process of claim 8, wherein the diluentcomprises isobutane, wherein the monomer comprises ethylene, wherein thecomonomer comprises propylene, 1-butene, 1-hexene, 1-octene, orcombinations thereof.
 10. The process of claim 1, further comprising:conveying the mixture downstream of the continuous take-off valve at atemperature less than a melting temperature of the olefin polymer. 11.The process of claim 1, wherein the olefin polymer comprisespolyethylene.
 12. The process of claim 11, wherein the olefin polymerfurther comprises a copolymer.
 13. The process of claim 1, wherein theolefin polymer comprises a linear low-density polyethylene.
 14. Theprocess of claim 1, wherein the continuous take-off valve has a nominaldiameter of about 1 inch to about 8 inches.
 15. A process for pressuremanagement of a polymerization product slurry withdrawn from a looppolymerization reactor in slurry polymerization, the process comprising:conveying the polymerization product slurry through a continuoustake-off valve; converting the polymerization product slurry to amixture upstream of a flashline heater, wherein the flash line heater isupstream of a vapor-liquid separator, wherein the mixture comprises atleast a portion of the liquid phase, the solid phase, and a vapor phase;and conveying the mixture through the flashline heater; wherein, atleast at one location downstream of the continuous take-off valve andupstream of a vapor-liquid separator, the mixture comprises a pressureless than a bubble point pressure of the liquid phase.
 16. The processof claim 15, wherein the liquid phase comprises a diluent, unreactedmonomer, unreacted comonomers, or combinations thereof.
 17. The processof claim 16, wherein the diluent comprises isobutane, wherein theunreacted monomer comprises ethylene, wherein the unreacted comonomercomprises propylene, 1-butene, 1-hexene, 1-octene, or combinationsthereof.
 18. The process of claim 15, wherein the vapor phase comprisesa vaporized portion of the liquid phase.
 19. The process of claim 15,wherein the solid phase comprises a solid polymer.
 20. The process ofclaim 19, further comprising: conveying the mixture through theflashline heater at a temperature less than a melting temperature of thesolid polymer.
 21. The process of claim 19, wherein the solid polymercomprises polyethylene.
 22. The process of claim 21, wherein the solidpolymer further comprises a polyethylene copolymer.
 23. The process ofclaim 21, wherein the polyethylene comprises a density in the range ofabout 0.905 g/cm³ to about 0.945 g/cm³.
 24. The process of claim 21,wherein the polyethylene comprises a linear low-density polyethylene.25. The process of claim 15, wherein the continuous take-off valve has anominal diameter of about 1 inch to about 8 inches.